IMPORTANCE IN AGRICULTURE:
With increasing hazards due to chemical, synthetic pesticides the only answer to mitigate these ill effects is use of safe alternatives. Amongst them use of natural enemies comprising of parasitoids, predators, entomopathogens etc. as biological control agents is the most effective environmentally sound and cost effective pest management approach to control insect pests. It is anticipated that biological control will play an increasingly important role in integrated pest management programs as broadspectrum pesticide use continues to decline.
The Importance of Parasitoid Wasps:
There are many species of parasitoid wasps but most are so tiny that they are rarely noticed. What they lack in size they make up in sheer numbers and efficiency and as a group they may be the single most important biological control method gardeners have. Wasps belong to the order Hymenoptera which includes more parasitoids than any other order of insects with thousands of parasitic species in over 40 families. Parasitoid wasps are very diverse in appearance ranging in size from as small as a fleck of pepper up to nearly 3 inch long and from uniformly dark in color to brightly colored and patterned. These tiny agents of death may be ectoparasitoids or endoparasitoids but the good news is, they do not sting people.
Important species in Maryland:
The most numerous and important species of parasitoid wasps in this area are in two superfamilies, Chalcidoidea (Chalcids) and Ichneumonoidea (Ichneumonoids). Among the more important Chalcid wasps are species in the Aphelinidae (Aphelinids), Chalcididae (Chalcidids), Encyrtidae (Encyrtids) and Trichogrammatidae (Trichogramma) families. The more important Ichneumonoid wasps are species in one of two families Braconidae (Braconids)and Ichneumonidae (Ichneumons) wasps.
The Importance of Parasitoids in Apple Orchards:
Sixty seven parasitoid species have been reared from leaf miner. The lowest number of parasitoid species occurred in the conventional orchard while the highest number were found in the integrated and in the untreated ones
Apple orchard sites and found that floral diversity within orchards may be buffering the negative effects of orchards being far from woodland. This suggests that both attributes flowering plant diversity in orchards and more areas of native woodland around farms are important for increasing beneficial insects and reducing pests. But higher flowering plant diversity may be even more important within orchards situated in intensive highly cleared landscapes.
As with most field ecology studies data are noisy because of all the natural variability going on. The random effect variance in some of our models was relatively high which suggests that those random effects were also having a big influence over the data. It appeared that orchard identity had a greater influence over pests syrphid flies and large predatory wasps while geographical region had a greater influence over wild bees and parasitoid wasps.
This complexity needs to be explored not ignored. It’s impossible to make definitive assumptions about how to manage a crop system based on data from one crop stage or one plant animal interaction. Studies that look at interactions between multiple pollinators pests and natural enemies within a system are valuable for science and agriculture and they are great fun to do.
Braconids:
Much of the aphid parasitoids are Hymenoptera of the family Braconidae. Their most active period corresponds to the rosy apple aphid infestation peak. They are exclusive solitary endoparasites of aphids. At the end of the development stage, the larva spins a cocoon inside the intact integument of its host.The efficiency of parasitoids in an open environment is still poorly documented notably since they are also the hosts of hyperparasitoids which limits the number of annual generations of primary parasitoids. This tomato hornworm is riddled with larva that have eaten their way through the skin to pupate. A wasp in the braconid family deposited eggs just beneath this caterpillar’s skin where the eggs developed until this point dining away at the insides of the caterpillar. When the pupae are mature and the adult wasps emerge, this caterpillar will die.
The possibility of having this beneficial wasp in the garden makes it worth keeping a few hornworms around.
APHIDS AND THEIR BIOCONTROL:
Aphids are small soft bodied insects that are common pests of nearly all indoor and outdoor field crops, vegetables, fruit trees and ornamental plants. There are different species of aphids some of which attack only one host plant while others attack numerous host plants. As well as causing direct damage by sucking sap and stunting growth and development essentially reflecting yield parameters they also act as potential vectors of plant viruses. The honeydew excreted by them occludes the stomatal openings of the leaves hampering photosynthesis and respiration and also favors the growth of black mold. Their prolific breeding, polyphagy advanced degree of polymorphism anholocyclic and holocyclic reproduction, parthenogenesis and telescopic generation, host alternation and polyvoltinism make them a notorious pest.
Concerns about the risks that chemical pesticides pose to the environment and human health as well as their increased costs have increased the need for more research into nonchemical methods of crop protection. In nature there are several organisms that feed, parasitize or infect aphids causing heavy mortality. Among those that regulate their populations are their parasitoids and predators that are commonly used in biocontrol programs in greenhouses and fields. The majority of aphid parasitoids belong to the subfamily Aphidiinae and a few species to Diptera. Aphid parasitoids have enormous potential that can be used in regulating the aphid population both in glasshouses and open fields. At present a number of parasitic species are utilized in biocontrol of aphids. A dozen species are commercially propagated and traded throughout the world more intensely in European countries and the United States. The constraints of biocontrol of aphids are multifold. The parasitoids are killed by their natural enemies. The biggest obstacle to the use of parasitoids in aphid control is their mass propagation at an affordable cost. Unless natural enemies are made as readily available biocontrol is likely to be a subject of academic interest with no practical role whatsoever. The potential for mass rearing of parasitoids is bright because new technologies are being developed to produce both aphids and parasitoids using artificial media. However there is a need to consider the trade off between producing and storing large quantities of parasitoids at low costs and the overall quality of the individuals that are released in crops. Measuring the fitness of mass-produced individuals remains a challenge and such a measure is likely to change depending on the attributes of the aphid species present and parasitoids that are released. Quantifying these parameters should increase the reliability of biocontrol programs and contribute to their acceptance by growers.
Ladybird beetles:
A good example of biological pest control might be the use of ladybirds in a greenhouse to reduce the numbers of whitefly an aphid that feeds on the crop plant. Ladybirds eat the aphids and so reduce their population below the EIL. In a greenhouse the control agents (ladybirds) cannot really escape into the wild and cause environmental damage and so the risk of the procedure is low. Sadly there are many examples from all over the world of a non-native control species being introduced to act against a specific pest and the biological control agent causing more harm than good through unpredictable behaviour in the new ecosystem. Biological control needs careful monitoring and detailed research in advance of the introduction of the new species.
Lacewings:
It is the larvae that destroy most of the pests. They are sometimes called aphid lions for their habit of dining on aphids. They also feed on mites other small insects and insect eggs. On spring and summer evenings lacewings can sometimes be seen clinging to porch lights and screens or windows.
